Accept an XML file containing a list of THM certificates instead of the

temporary solution using the raw public key

Change-Id: I6f9543c39e328503db0f24a49901fff6e04fe8c5
Test: adb shell am instrument -w -e package \
com.android.server.locksettings.recoverablekeystore \
com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner